1 The idea
A keyframe is a value you set on a frame; the software fills in the frames between (interpolation). Constant holds the value, then jumps. Linear moves at one speed all the way. Ease in-out starts slowly, speeds up mid-way and slows before it arrives. Ease out starts fast and slows to a stop.
Read the onion-skin dots: far apart = fast, close together = slow. The graph below is value over time, and its slope is the speed. Work out which interpolation the target box uses and on which frame it arrives.
ease in-out: v = 3u² − 2u³ · u = frame ÷ (frame of key 2)2 Hands-on
Task: make your box sit on the target box on every frame
Check whether the target’s dots bunch up at one end or both, and from which frame its curve goes flat
3 Deep dive
Keys are instructions; the frames between are a guess
You only tell the software “frame 0 is here, frame 16 is there”; it picks everything else from the interpolation you set. Changing the interpolation changes every in-between frame while the keys don’t move at all.
In comp you key far more than position: glow brightness, blur size, element opacity. The same rules apply to every number.
| Type | Speed at key 1 | Speed at key 2 | Use for |
|---|---|---|---|
| constant | 0 (holds) | jumps | on/off, switches, flicker |
| linear | 1 | 1 | steady spins, constant drifts |
| ease in-out | 0 | 0 | from rest to rest |
| ease out | 2 | 0 | fly in and settle |
Reading motion from dots
Onion skin shows every frame’s position at once. The gap between dots is the distance moved in one frame, which is speed. Linear gives even gaps; ease in-out bunches dots at both ends and spreads them in the middle.
Ease in-out peaks at 1.5× the average speed mid-way, to make up for the slow start and end. With the same duration, an ease looks punchier in the middle than linear.
- 1Set the keys
- 2Pick the interpolation
- 3Read onion skin / graph
- 4Play at real speed
Example: a title card sliding over the desert plate
The card slides from the frame edge and stops above a rock. Linear brakes like a crash. Ease out flies in and settles softly. Ease in-out looks as if the card started from rest off screen, which is often too slow for a card that should arrive briskly.
Things entering from off screen: ease out. Things leaving: ease in.
4 In real work
In Nuke
- Right-click a knob (for example a Transform’s translate) > Set key to key it on the current frame.
- Open the Curve Editor, select keys, right-click > Interpolation to pick Constant, Linear, Smooth, Horizontal and others.
- Use the Dope Sheet to slide the timing of keys without changing their values.
- Watch the Transform’s motion path in the Viewer to see the spacing frame by frame.
Common mistakes → the fix
- ✗ Leaving the default interpolation without looking at the curve✓ Open the curve after keying and check the slopes in and out are what you meant.
- ✗ Using linear on something that starts or ends at rest✓ Ease the ends that are at rest; linear suits only continuous motion.
- ✗ Keying every frame by hand to make it “smooth”✓ Use as few keys as possible and shape them with interpolation. Dense keys are hard to edit and often jitter.
- ✗ Accidentally using constant on a value that should flow✓ If a value jumps in one frame, check the interpolation of the key before it.
Before you send the shot
- Every keyed curve has no unintended sharp corners
- Ends at rest are eased; continuous motion is linear
- As few keys as the move needs
- Judged at real speed, not by stepping frames
5 Check yourself
You keyed a text card to slide in and stop, but it jumps to the end in a single frame. Most likely why?
🔒 Answer the question above and this card opens
1. Over the same duration as linear, what is the peak speed of an ease in-out compared with linear?
2. An LED blinking on and off in a comp: which interpolation?
Where the numbers come from: Ease in-out here is a cubic Hermite with flat tangents (3u² − 2u³) and ease out is 1 − (1 − u)²: common example curves. Each app has its own curves and names. “Ease out” follows the CSS and motion-graphics convention (slows at the end); some apps name the side of the key instead, so the meaning can flip. Animations are drawn in code at 24 fps.